Acids and Bases Activity

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Acids and Bases


Activity:


  1. Distribute water molecules and hydrochloric acid molecules.
  2. Ask them to react the hydrochloric acid molecules with water to produce hydronium and chloride ions. A proton was donated by the HCl to the solution, it is an acid; water, acting as a base, accepts the proton. Hydrochloric acid is a strong acid so it should dissolve completely.
  3. Retrieve hydrochloric acid molecules and hand out ammonia molecules.
  4. Ask the class to carry out a reaction between the ammonia and water molecules. Ammonia is a stronger base than water in this reaction and thus it accepts protons from water molecules to make ammonium ions. Water acts as an acid by donating its protons. Ammonia is a weak base, so the reaction should be in dynamic equilibrium with some ammonium ions donating protons back into solution.
  5. Retrieve ammonia molecules and hand out acetic acid molecules.
  6. Acetic acid is a weak acid and does not dissociate completely in water.
  7. Ask the class to carry out a reaction between acetic acid and water and they will notice that not all the acetic acid molecules will ionize and only some will donate protons and produce the conjugate base acetate.

Summary:

  • A Bronsted-Lowry acid is a proton donor while a base is a proton acceptor.
  • Water can act as both an acid and a base as it can autoionize into hydronium and hydroxide depending on how strong of a base the acid or base it is reacting with is.
  • Bronsted-Lowry theory describes acid and base reactions as a competition for protons by bases. The stronger the base, the greater its affinity for protons will be. As a result, water can be an acid or a base depending on how strong of a base the other molecule is.
  • Strong acids have very weak conjugate bases. Strong acids and strong bases dissociate completely in water. Weak acids and weak bases dissociate at a very low percentage in water.
  • Every acid-base reaction involves conjugate acid-base pairs. Conjugate acid-base pairs are the molecules in a reaction that differ by a single proton. For example, the conjugate base of acetic acid is acetate and the conjugate acid of the base ammonia is the ammonium ion.